The use of semiconductor integrated circuit chips for data storage, such as portable flash memory cards, is widespread. Users of these devices desire ever-increasing data storage capacity, and manufacturers strive to provide a large storage capacity in a cost-effective manner.
It is known to achieve an increased memory density within a single package by stacking multiple semiconductor chips or dice in a single package, known as a Multi-Chip Package (MCP). The increased number of dice provides a corresponding increase in storage capacity relative to a single die. Referring to FIG. 1, the MCP 100 consists of four NAND Flash memory dice 102. It should be understood that this method is equally applicable to other memory devices. Each die 102 has bonding pads 104 that are electrically connected via bonding wires 106 to a common substrate 108. Although the dice 102 are shown with bonding pads 104 on two opposite sides, it should be understood that each die 102 may alternatively have a different arrangement of bonding pads 104, for example on a single side, or on two adjacent sides, or any other arrangement. The substrate 108 provides further electrical connections from the bonding wires 106 to solder balls 110 on the opposite side of the substrate 108, forming a Ball Grid Array (BGA) for connection to an external device (not shown). An interposer 112 is provided between each pair of consecutive dice 102, to create a sufficient clearance therebetween to allow the attachment of the bonding wires 106 to the bonding pads 104.
Another approach is shown in FIG. 2. The MCP 200 consists of four NAND Flash memory dice 202 with bonding pads 204 along one side. The dice 202 are laterally offset from one another to expose the bonding pads 204 of each die 202. In this arrangement, all of the dice 202 can be stacked in a single step, and thereafter all of the bonding wires 206 can be attached in a single step by a wire bonding machine (not shown). This arrangement does not require interposers to provide access to the bonding pads 204, resulting in a more compact arrangement. This arrangement may alternatively be used with dice 202 having bonding pads 204 along two adjacent sides, in which case the dice would be laterally offset in two dimensions.
In these and other arrangements, each die consumes power during operation, which is dissipated as heat. An accumulation of heat within the stack can cause reduced operating efficiency, or even failure of the device. A number of manufacturing trends that provide increased performance or capacity also tend to generate more heat in a smaller volume, such as an increased number of dice, decreased die thickness, decreased feature size, and increased clock speed. Therefore, it is increasingly important to discharge the heat from within the stack to the environment.
One approach is to provide a thermally conductive heat sink with a planar surface in thermal contact with a top or bottom die of the stack. The heat from the stack is conducted into the heat sink, and from there to the environment. This approach provides cooling for the top or bottom surface of the stack. However, cooling the middle layers of the stack remains a problem because the middle layers are farther from the surface heat sink and surrounded by other heat-generating dice.
Another approach is to provide each die in a dielectric carrier, as shown in U.S. Pat. No. 5,600,541. The dielectric carrier permits stacking of the dice and allows electrical connections to be made by wires or vias running through the dielectric, but may contribute significantly to the overall thickness of the stack. In addition, the electrical connections to the die may increase the expense and complexity of assembly, and even the most thermally-conductive dielectric materials are somewhat limited in their capacity to dissipate heat, which may not be sufficient for some applications.
Still another approach is to provide an active cooling system, such as by circulating a liquid coolant around or through the die stack, for example through vias. However, if the active cooling system fails the device is also likely to fail, particularly since actively-cooled systems are generally not equipped to passively dissipate a sufficient amount of heat.
Therefore, there is a need for a Multi-Chip Package having improved heat dissipation.
There is also a need for a Multi-Chip Package having a compact arrangement.
There is also a need for a Multi-Chip Package that is simple to manufacture.